Complex types client can ignore isoptional fields for structure (#1503)

fixes #1476 
 Improve IOP, some recent ModelCompiler versions (starting with errata 1.04.9) produce invalid output and all IsOptional fields have become true by default, causing the complex types client to bail out for Structures created with this ModelCompiler release. However, the IsOptional field can be ignored.
ModelCompiler is fixed in 1.04.10 and greater

Libraries/Opc.Ua.Client.ComplexTypes/ComplexTypeSystem.cs

@@ -685,11 +685,6 @@ private StructureDefinition GetStructureDefinition(DataTypeNode dataTypeNode)
                     {
                         return null;
                     }
-                    if (structureDefinition.StructureType == StructureType.Structure &&
-                        field.IsOptional)
-                    {
-                        return null;
-                    }
                 }
                 return structureDefinition;
             }